file_manager: Add a unit test for FindAllTypesOfTasks()

Along the way, add a parameter to FindAllTypesOfTasks() to make this
function testable.

BUG=269929
TEST=none
R=kinaba@chromium.org

Review URL: https://codereview.chromium.org/26221007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228116 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228116
FileAPI: {Open,Delete}FileSystem should run on IO thread

FileSystemContext::{Open,Delete}FileSystem should run on IO thread, but some
tests violate the rule. This forces these tests to follow the rule.


BUG=none
TEST=unit_tests --gtest_filter=LocalFileSyncContextTest.*
TEST=unit_tests --gtest_filter=SyncFileSystemServiceTest.*

Review URL: https://codereview.chromium.org/25209002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228117 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 228117